Aircraft: GOLDEN EAGLE 421
Phase of flight: Final Approach
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy

I was on Local Control when Aircraft Y called up requesting a SVFR clearance to the East of the airport. Ceiling was over 2;500 FT AGL but visibility was at 1 1/2 to 2 1/2 SM. I approved SVFR in Class D airspace. I noticed an IFR inbound tracking south of the airfield for vectors to ILS 19. I knew I had time before I had to restrict or separate Aircraft Y. I told Aircraft Y about the IFR traffic and that he would have to land or exit the Delta in a few minutes. Aircraft Y said he could possibly land on sight and that he was assisting local rescue personnel in search of an individual in the river east of the field. CIC then called ZZZ let them know we had a situation and might need to send Aircraft X around. They called back to tell us Aircraft X was low on fuel. I asked for advice from CIC. We got a position report from Aircraft Y though he never appeared on RADAR because of his altitude; I allowed Aircraft X to land. Given the position report; I and the CIC felt assured that there was safe distance between both aircraft and did not want to restrict either because of the low fuel status of Aircraft X and the search and rescue assist by Aircraft Y. Aircraft X landed without incident; and Aircraft Y also landed a little while later without incident. We have no LOA in place with our local helicopter operators; we could not legally separate the SVFR and IFR aircraft. If such procedures had been in place; this incident would not have occurred. IFR; snow; 1 1/2 mile visibility and low ceilings. Aircraft Y; normally a news helicopter; requested and was cleared to depart the airport to the East; SVFR; to work within the Class D. A couple minutes later; we noticed on RADAR that ZZZ Approach was vectoring an IFR Twin Cessna for the ILS 19 at our airport. We knew that in about 10 minutes or so the twin would be within 3 miles of the SVFR helicopter; and that we'd have to ask the helicopter to exit the Delta or land momentarily until the twin landed. I told LC to advise Aircraft Y of this; as a heads-up. He did; and Aircraft Y replied that he was assisting in rescuing somebody from the river. Well; that changed things. I decided then that I was not going to move the helicopter. So I called ZZZ and advised that we might have to send the twin around for a re-sequence; depending on where Aircraft Y was when the twin got close; for separation purposes. ZZZ said he'd let the twin know. A minute later ZZZ called back and said that the pilot of the twin reported low on fuel. So now I don't want to move the twin either. What? Send a low-fuel prop-job around to fly another 30 miles in possible icing conditions? Nope. So at the proper time I asked LC to get a position report from the Aircraft Y. Aircraft Y was below RADAR coverage during his entire SVFR operation; and we know that we lose RADAR coverage around 011 MSL. Aircraft Y reported about a mile east of the river bridge. I knew that the bridge was at least a mile East of the airport; but not more than 2. I also knew that even if the Twin went NORDO and went missed approach; he still could not go left (East) because both the published missed approach procedure and the standard climb-out-in-lieu-of procedure used an initial right hand climbing turn. Plus; with Aircraft Y being SVFR under low ceilings; I knew he could not climb above the tops of the obstructions surrounding him. What this means is that I knew that the operation was going to be safe (the twin and the helicopter were NOT going to be getting together); but I also knew that there was probably not going to be 3 miles between them when altitude separation was lost. I knew that on the front side; and chose to run the operation anyway; because I believed that an emergency situation may result from sending the twin around; and knew that an emergency situation of sorts already existed with Aircraft Y. Both aircraft landed without incident. The 7110.65; chapter 7; allows for reduced SVFR separation with helicopters if there is an LOA with the helicopter operators detailing the reduced minima. I've been clamoring for such an LOA for years; and nobody's really bothered with it. Had we had an LOA like that in place; I would not be filing this report; because I could have easily ensured the reduced minima. I don't particularly appreciate being in a tight spot where I have to break the rules to do the right thing; when we could have had the rules adapted to our local situation years ago; allowing me to do the right thing legally. Tower Controller described a loss of separation event when a SVFR helicopter on a rescue mission was less than the required distance from an IFR inbound with minimum fuel. The reporter suggested a new LOA would have assisted in this case.